MAXIM MAX1762, MAX1791 User Manual

General Description

The MAX1762/MAX1791 PWM step-down controllers provide high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high-voltage batteries to generate low-voltage CPU core, I/O, and chipset RAM supplies in notebook computers and PDAs.

Maxim’s proprietary Quick-PWM™ pulse-width modulator is a free-running constant on-time type with input feed-forward. Its high operating frequency (300kHz) allows small external components to be utilized in PC board area-critical applications such as subnotebook computers and smart phones. PWM operation occurs at heavy loads, and automatic switchover to pulse-skipping operation occurs at lighter loads. The external high-side p-channel and low-side n-channel MOSFETs require no bootstrap components. The MAX1762/ MAX1791 are simple, easy to compensate, and do not have the noise sensitivity of conventional fixed-frequency current-mode PWMs.

These devices achieve high efficiency at a reduced cost by eliminating the current-sense resistor found in traditional current-mode PWMs. Efficiency is further enhanced by their ability to drive synchronous-rectifier MOSFETs. The MAX1762/MAX1791 come in a 10-pin µMAX package and offer two fixed voltages (Dual Mode™) for each device, 1.8V/2.5V/adj (MAX1762) and

3.3V/5.0V/adj (MAX1791).

________________________Applications

Notebooks Handy-Terminals

Subnotebooks PDAs

Digital Cameras Smart Phones

1.8V/2.5V Logic and I/O Supplies

Features

♦ High Operating Frequency (300kHz)

♦ No Current-Sense Resistor

♦ Accurate Current Limit

♦ ±1% Total DC Error over Line and During

Continuous Conduction

♦ Dual Mode Fixed Output

1.8V/2.5V/adj (MAX1762)

3.3V/5.0V/adj (MAX1791)

♦ 0.5V to 5.5V Output Adjust Range

♦ 5V to 20V Input Range

♦ Automatic Light-Load Pulse Skipping Operation

♦ Free-Running On-Demand PWM

♦ Foldback Mode™ UVLO

♦ PFET/NFET Synchronous Buck

♦ 4.65V at 25mA Linear Regulator Output

♦ 5µA Shutdown Supply Current

♦ 230µA Quiescent Supply Current

♦ 10-Pin µMAX Package

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down

Controllers for Notebooks

________________________________________________________________ Maxim Integrated Products 1

19-1923; Rev 1; 10/05

EVALUATION KIT

AVAILABLE

Ordering Information

PART TEMP RANGE

PIN-PACKAGE

MAX1762EUB -40°C to +85°C 10 µMAX MAX1791EUB -40°C to +85°C 10 µMAX

GND

OUT

REF

SHDN

BATT

(5V TO 20V)

OUT

1.8V/3.3V

MAX1762 MAX1791

Typical Operating Circuit

DLOUT

REF

MAX1762 MAX1791

µMAX

TOP VIEW

GNDSHDN

Pin Configuration

For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Quick-PWM, Dual Mode, and Foldback Mode are a trademarks of Maxim Integrated Products, Inc.

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

VP, SHDN to GND ..................................................-0.3V to +22V

VP to VL ..................................................................-0.3V to +22V

OUT, VL to GND .......................................................-0.3V to +6V

DL, FB, REF to GND ....................................-0.3V to (VL + 0.3V)

DH to GND....................................................-0.3V to (VP + 0.3V)

CS to GND ....................................................-2.0V to (VP + 0.3V)

REF Short Circuit to GND ...........................................Continuous

Continuous Power Dissipation (T

= +70°C)

10-Pin µMAX (derate 5.6mW/°C above +70°C) ...........444mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

ELECTRICAL CHARACTERISTICS

(VVP= 15V, VL enabled, CVL= 1µF, C

REF

= 0.1µF,

= 0 to +85°C,

unless otherwise noted. Typical values are at T

= +25°C.)

(Note 1)

PARAMETER

CONDITIONS

UNITS

VP Input Voltage Range V

520V

VL Input Voltage Range V

VL (overdriven)

OUT Output Voltage (MAX1762, 1.8V Fixed)

OUT

VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = GND, continuous conduction mode

1.8

OUT Output Voltage (MAX1762, 2.5V Fixed)

OUT

VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = VL, continuous conduction mode

2.5

OUT Output Voltage (MAX1791, 3.3V Fixed)

OUT

VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = GND, continuous conduction mode

3.3

OUT Output Voltage (MAX1791, 5V Fixed)

OUT

VVP = 7V to 20V, VVL = 4.75V to 5.25V, FB = VL, continuous conduction mode

OUT Output Voltage (Adj Mode)

VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = OUT, continuous conduction mode

Output Voltage Adjust Range 0.5 5.5 V

OUT Input Resistance Adjustable-output mode

kΩ

FB Input Bias Current VFB = 1.3V

0.1 µA

Soft-Start Ramp Time Zero to full I

LIM

µs

OUT

= 1.25V, VVP = 6V

On-Time (Note 2) t

OUT

= 5V, VVP = 6V

Minimum Off-Time t

OFF

(Note 2)

VL Quiescent Supply Current

FB = GND, V

= 5V, OUT forced above the

regulation point

µA

VVL = float

VP Quiescent Supply Current

FB = GND, OUT forced above the regulation point, V

= 20V

= 5V 93

µA

VL Shutdown Supply Current VVL = 5V, SHDN = GND 2 15 µA

VP Shutdown Supply Current

412µA

VL Output Voltage I

LOAD

= 0 to 25mA, VVP = 5V to 20V 4.5

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

SYMBOL

MIN TYP MAX

S HD N = GN D , m easur ed at V P , V

= 0 or 5V

V L

4.75 5.25

1.773

2.463

3.250

4.925

1.231 1.250 1.269

300 800 1700

-0.1

666 740 814

2550 2830 3110

300 400 500

1700

153 260

227 410

4.65 4.75

1.827

2.538

3.350

5.075

200

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down

Controllers for Notebooks

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VVP= 15V, VL enabled, CVL= 1µF, C

REF

= 0.1µF,

= 0 to +85°C,

unless otherwise noted. Typical values are at T

= +25°C.)

(Note 1)

PARAMETER

CONDITIONS

UNITS

Reference Voltage VVL = 4.75V to 5.25V, no load

Reference Load Regulation I

REF

= 0 to 50µA

REF Sink Current REF in regulation 10 µA

REF Fault Lockout Voltage Falling edge 1.6 V

Output Undervoltage Threshold (Foldback)

With respect to regulation point, no load 60 70 80 %

Output Undervoltage Lockout Time (Foldback)

From SHDN signal going high V

OUT

< 0.6 x

regulation point

10 20 42 ms

Current-Limit Threshold V

ILIM

-90

Thermal Shutdown Threshold Hysteresis = 10oC

VL Undervoltage Lockout Threshold

Rising edge, hysteresis = 20mV, PWM disabled below this level

4.1 4.4 V

DH Gate Driver On-Resistance VVP = 6V to 20V, measure at 50mA 5 8 Ω

DL Gate Driver On-Resistance (Pullup)

DL, high state, measure at 50mA 5 8 Ω

DL Gate Driver On-Resistance (Pulldown)

DL, low state, measure at 50mA 1 5 Ω

DH Gate Driver Source/Sink Current

= 3V, VVP = 6V 0.6 A

DL Gate Driver Sink Current VDL = 2.5V 0.9 A

DL Gate Driver Source Current V

= 2.5V 0.5 A

SHDN Logic Input High Threshold Voltage

1.6 V

SHDN Logic Input Low Threshold Voltage

0.6 V

MAX1762 V

OUT

= 1.8V fixed

MAX1791 V

OUT

= 3.3V fixed

MAX1762 V

OUT

= 2.5V fixed

Dual Mode Threshold Voltage

MAX1791 V

OUT

= 5V fixed

2.5

SHDN Logic Input Current SHDN = 0 or 5V -2 +2 µA

SYMBOL

MIN TYP MAX

1.98

-100 -110

160

100 150

3.25

2.02

0.01

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS

(VVP= 15V, VL enabled, CVL= 1µF, C

REF

= 0.1µF,

= -40 to +85°C,

unless otherwise noted.) (Note 1)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

VP Input Voltage Range V

520V

VL Input Voltage Range V

VL (overdriven)

OUT Output Voltage (MAX1762, 1.8V Fixed)

OUT

VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = GND, continuous conduction mode

OUT Output Voltage (MAX1762, 2.5V Fixed)

OUT

VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = VL, continuous conduction mode

OUT Output Voltage (MAX1791, 3.3V Fixed)

OUT

VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = GND, continuous conduction mode

OUT Output Voltage (MAX1791, 5V Fixed)

OUT

VVP = 7V to 20V, VVL = 4.75V to 5.25V, FB = VL, continuous conduction mode

OUT Output Voltage (adj Mode)

VVP = 5V to 20V, VVL = 4.75V to 5.25V, FB = OUT, continuous conduction mode

FB Input Bias Current VFB = 1.3V

0.2 µA

OUT

= 1.25V, VVP = 6V

On-Time (Note 2) t

OUT

= 5V, VVP = 6V

Minimum Off-Time t

OFF

(Note 2)

VL Quiescent Supply Current

FB = GND, V

= 5V, OUT forced above the

regulation point

µA

VP Quiescent Supply Current

FB = GND, OUT forced above the regulation point V

= 20V

µA

VL Shutdown Supply Current VVL = 5V, SHDN = GND 15 µA

VP Shutdown Supply Current

12 µA

VL Output Voltage I

LOAD

= 0 to 25mA, VVP = 5V to 20V 4.5

Reference Voltage VVL = 4.75V to 5.25V, no load

Reference Load Regulation I

REF

= 0 to 50µA

REF Sink Current REF in regulation 10 µA

Output Undervoltage Threshold (Foldback)

With respect to regulation point, no load 60 80 %

Output Undervoltage Lockout Time (Foldback)

From SHDN signal going high, V

OUT

< 0.6 x

regulation point

10 42 ms

Current-Limit Threshold V

ILIM

-90

4.75 5.25

1.773 1.827

2.463 2.538

3.250 3.350

4.925 5.075

1.231 1.269

S HD N = GN D , m easur ed at V P , V

= float 410

V L

= 5V 200

V L

= 0 or 5V

V L

-0.2

666 814

2550 3110

250 550

1.98 2.02

260

4.75

0.01

-110

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down

Controllers for Notebooks

_______________________________________________________________________________________ 5

Note 1:

Specifications to -40°C are guaranteed by design, not production tested.

Note 2:

One-shot times are measured at the DH pin (VP = 15V, C

= 400pF, 90% point to 90% point; see drawing below for

measurement details).

ELECTRICAL CHARACTERISTICS (continued)

(VVP= 15V, VL enabled, CVL= 1µF, C

REF

= 0.1µF,

= -40 to +85°C,

unless otherwise noted.) (Note 1)

PARAMETER

CONDITIONS

UNITS

VL Undervoltage Lockout Threshold

Rising edge, hysteresis = 20mV, PWM disabled below this level

4.1 4.4 V

SHDN Logic Input High Threshold Voltage

1.6 V

SHDN Logic Input Low Threshold Voltage

0.6 V

MAX1762 V

OUT

= 1.8V fixed

MAX1791 V

OUT

= 3.3V fixed

MAX1762 V

OUT

= 2.5V fixed

Dual Mode Threshold Voltage

MAX1791 V

OUT

= 5V fixed

2.5 4 V

90% 90%

SYMBOL

MIN TYP MAX

150

MAX1762/MAX1791

High-Efficiency, 10-Pin µMAX, Step-Down Controllers for Notebooks

6 _______________________________________________________________________________________

Typical Operating Characteristics

(TA = +25°C, unless otherwise noted.)

100

0.1 1 10 100 1000 10,000

MAX1762

EFFICIENCY vs. LOAD (2.5V)

MAX1762/91 toc01

LOAD CURRENT (mA)

EFFICIENCY (%)

VVP = 5V

VVP = 12V

VVP = 7V

VVP = 18V

100

0.1 1 10 100 1000 10,000

MAX1791

EFFICIENCY vs. LOAD (3.3V)

MAX1762/91 toc05

LOAD CURRENT (mA)

EFFICIENCY (%)

VVP = 18V

VVP = 12V

VVP = 7V

VVP = 5V

100

0.1 1 10 100 1000 10,000

MAX1791

EFFICIENCY vs. LOAD (3.0V)

MAX1762/91 toc06

LOAD CURRENT (mA)

EFFICIENCY (%)

VVP = 7V

VVP = 18V

VVP = 12V

VVP = 5V

-0.6

-0.4

-0.5

-0.2

-0.3

-0.1

0.1

0105152025

VL VOLTAGE ERROR vs. OUTPUT CURRENT

MAX1762/91 toc08

VL CURRENT (mA)

VL VOLTAGE ERROR (%)

VVP = 12V

OUT

= 2.5V

100

0.1 1 10 100 1000 10,000

MAX1791

EFFICIENCY vs. LOAD (5V)

MAX1762/91 toc04

LOAD CURRENT (mA)

EFFICIENCY (%)

VVP = 7V

VVP = 18V

VVP = 12V

250

275

325

300

350

375

FREQUENCY vs. SUPPLY VOLTAGE

MAX1762/91 toc07

SUPPLY VOLTAGE (V)

FREQUENCY (kHz)

51181417

OUT

= 3.3V

OUT

= 5.0V

OUT

= 2.5V

OUT

= 1.8V

LOAD = 1A

100

0.1 1 10 100 1000 10,000

MAX1762

EFFICIENCY vs. LOAD (1.8V)

MAX1762/91 toc02

LOAD CURRENT (mA)

EFFICIENCY (%)

VVP = 18V

VVP = 12V

VVP = 5V

VVP = 7V

100

0.1 1 10 100 1000 10,000

MAX1762

EFFICIENCY vs. LOAD (1V)

MAX1762/91 toc03

LOAD CURRENT (mA)

EFFICIENCY (%)

VVP = 7V

VVP = 12V

VVP = 5V

VVP = 18V

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